1. Field of the Invention
The invention relates to an improved process for dyeing human hair, involving the production of progressively deeper colorations with succeeding treatments for attaining a target shade, and the maintenance thereof by further treatments at appropriate intervals thereafter.
2. The Prior Art
Dyeing of human hair has been effected heretofore by application of water-soluble heavy metal compounds -- e.g. of Ni or Pb -- together with reagents yielding a dark-colored water-insoluble metal derivative with the metal compound -- e.g. pyrogallol or sulfur compounds.
A more versatile dyeing process -- with which the present invention is concerned -- involves application to hair of oxidizable primary aromatic amines (especially diamines) and substitution products thereof, usually together with aminophenols, in admixture with an oxidizing agent -- especially H.sub.2 0.sub.2 or its derivatives, such as urea peroxide, perborates, percarbonates, persulfates, perphosphates, periodates or the like -- whereby socalled oxidation dyes or colors are formed in situ on the hair (cf. U.S. Pat. No. 3,649,159). While other oxidizing agents such as FeCl.sub.3, iodates, permanganates or bichromates can be employed, H.sub.2 O.sub.2 and its derivatives are more generally used. In the color-forming reaction, the aromatic primary amino groups and phenolic hydroxyl groups are oxidized in situ to form imino groups and CO groups, and coupling occurs to form polyimino compounds in which the aromatic nuclei assume a quinonoid configuration -- e.g. ##STR1## It is customary also to include in the colorant mixture, coupling compounds such as a polyhydric phenol -- e.g. resorcinol, pyrogallol or the like. In general, at least a molecular equivalent or in excess thereof of the oxidizing reagent, relative to the oxidizable diamine or aminophenol, is employed, although somewhat lesser proportions of oxidant can be employed. Atmospheric oxygen can be relied upon as the sole oxidant in hair dyeing, but the use of H.sub.2 O.sub.2 or its derivatives is generally preferred, since the reaction proceeds more rapidly with the latter oxidants and can be more readily controlled. Compositions yielding oxidation colors are conventionally combined with surfactants (detergents, wetting agents) and thickeners, such as are usual in shampoos, so as to facilitate removal of excess reagents by rinsing. Amine and aminophenol colorant mixtures and oxidants can be applied to hair successively in a two-step process, or they can be pre-mixed before application to the hair.
Women generally prefer a dyeing process in which the target color is attained in a single treatment -- usually involving application of colorant mixture and oxidant in suitable proportions for the target color, allowing the development reaction to proceed for e.g. 15 - 60 minutes, and then washing out the excess reagents. Men, however, are usually reluctant to dye their hair in such a way that the complete color change occurs in a single treatment, since they find this embarrassing. A number of preparations have been marketed for men which gradually change or darken the color by repeated applications of the dyeing composition at selected intervals, and maintenance of the final desired coloration is effected by further applications at less frequent intervals. Such coloring compositions usually employ a heavy metal compound and a reagent adapted to form a dark colored sulfide of the metal. However, as compared with oxidation dyes, these compositions lack versatility in the hue of the available colorations.
It was known heretofore to produce gradual darkening of hair by repeated application of an oxidation color mixture at successive intervals, relying upon oxidation by atmospheric oxygen to develop the coloration (cf. U.S. Pat. No. 3,920,384). It was also known to modify the depth of shade by varying the concentration of the colorant (cf. U.S. Pat. Nos. 305,057, 1,019,576, 2,185,467, 3,128,232 and Br. Pat. No. 12,902/99), not only with oxidation color mixtures, but also with pyrogallol-Ni salt mixtures and direct dyes. Depth of shade has also been controlled by increasing the duration of the treatment, utilizing phthalaldehyde combined with an alkylolamine as the colorant mixture (cf. U.S. Pat. No. 3,871,818). Using a trihydric phenol as the colorant with an iodate, periodate or persulfate as an oxidant therefor, it was known to increase the depth of shade of the coloration produced by increasing the oxidant concentration -- the oxidant and colorant being applied in the same or separate solutions (cf. U.S. Pat. No. 2,975,101).
Processes heretofore known using aromatic primary amines and aminophenols as oxidation colorants for hair do not suggest varying the proportion or concentration of the oxidant as a means for controlling depth of shade. Thus, it was known to add equal volumes of 1% and 5% solutions of a perphosphate to similar volumes of an oxidation colorant mixture (cf. U.S. Pat. No. 3,649,159), whereby however the same shade was obtained -- the development time being 20 minutes in the case of the more concentrated oxidant, and 40 - 60 minutes in the case of the more dilute oxidant. No change was observed in the coloration or rate of development when 2% H.sub.2 O.sub.2 or 5% NaBO.sub.3.H.sub.2 O was included with the perphosphate. U.S. Pat. No. 3,666,812 notes that increased quantities of H.sub.2 O.sub.2 and NH.sub.3 with oxidation colorants decolorizes the hair and produces a desired shade, but fails to suggest that deeper shades could result from an increase in the proportion of oxidant. In a process using a diaminonitrobenzene as the colorant, equal volumes of 1% and 9% H.sub.2 O.sub.2 yielded shades which were similar, or in some cases, lighter in hair dyeing when the higher concentration of oxidant was employed (cf. U.S. Pat. No. 3,907,494).